Prediction of the Nozzle Flow and Jet Characteristics at Start and End of Injection: Transient Behaviors

This paper reports investigations on diesel jet transients, accounting for internal nozzle flow and needle motion. The calculations are performed with Large Eddy Simulation (LES) turbulence model by coupling the internal and external multiphase flows simultaneously. Short and multiple injection strategies are commonly used in internal combustion engines. Their features are significantly different from those generally found in steady state conditions, which have been extensively studied in the past, however, these conditions are seldom reached in modern engines. Recent researches have shown that residual gas can be ingested in the injector sac after the end-of-injection (EOI) and undesired dribbles can be produced. Moreover, a new injection event behaves differently at the start-of-injection (SOI) depending on the sac initial condition, and the initial spray development can be affected for the first few tens of μs. To investigate these phenomena, LES of end-of-injection and start-of-injection processes have been carried out on a single hole injector, in order to provide insights in to the physics. Detailed needle motion data and orifice morphology have been measured using x-ray synchrotron source at Argonne National Laboratory. Simulations are validated against available x-ray data of the internal flow and near nozzle exit region. Results are able to realistically capture the injection rate ramp-up, the initial gas discharge followed by liquid injection, the realistic liquid tip penetration and the EOI dribbles, provided all the boundary condition details are properly included in the simulations. Such information is invaluable towards developing simulation tools for enabling and improving low temperature combustion concepts with multiple injection strategies.